[RFC PATCH 0/6] [RFC] Faultable tracepoints (v2)

[Michael Jeanson]

Formerly known as “Sleepable tracepoints”.

When invoked from system call enter/exit instrumentation, accessing
user-space data is a common use-case for tracers. However, tracepoints
currently disable preemption around iteration on the registered
tracepoint probes and invocation of the probe callbacks, which prevents
tracers from handling page faults.

Extend the tracepoint and trace event APIs to allow specific tracer
probes to take page faults. Adapt ftrace, perf, and ebpf to allow being
called from sleepable context, and convert the system call enter/exit
instrumentation to sleepable tracepoints.

This series only implements the tracepoint infrastructure required to
allow tracers to handle page faults. Modifying each tracer to handle
those page faults would be a next step after we all agree on this piece
of instrumentation infrastructure.

This patchset is based on v5.10.15.

Changes since v1 RFC:

  - Rename "sleepable tracepoints" to "faultable tracepoints", MAYSLEEP to
    MAYFAULT, and use might_fault() rather than might_sleep(), to properly
    convey that the tracepoints are meant to be able to take a page fault,
    which requires to be able to sleep *and* to hold the mmap_sem.

Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Yonghong Song <yhs@xxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: bpf@xxxxxxxxxxxxxxx

Mathieu Desnoyers (1):
  tracing: use Tasks Trace RCU instead of SRCU for rcuidle tracepoints

Michael Jeanson (5):
  tracing: introduce faultable tracepoints (v2)
  tracing: ftrace: add support for faultable tracepoints
  tracing: bpf-trace: add support for faultable tracepoints
  tracing: perf: add support for faultable tracepoints
  tracing: convert sys_enter/exit to faultable tracepoints

 include/linux/tracepoint-defs.h |  11 ++++
 include/linux/tracepoint.h      | 111 +++++++++++++++++++++-----------
 include/trace/bpf_probe.h       |  23 ++++++-
 include/trace/define_trace.h    |   8 +++
 include/trace/events/syscalls.h |   4 +-
 include/trace/perf.h            |  26 ++++++--
 include/trace/trace_events.h    |  79 +++++++++++++++++++++--
 init/Kconfig                    |   1 +
 kernel/trace/bpf_trace.c        |   5 +-
 kernel/trace/trace_events.c     |  15 ++++-
 kernel/trace/trace_syscalls.c   |  84 ++++++++++++++++--------
 kernel/tracepoint.c             | 104 ++++++++++++++++++++++++------
 12 files changed, 373 insertions(+), 98 deletions(-)

-- 
2.25.1